Susceptor for epitaxial growth and epitaxial growth method

ABSTRACT

A susceptor for use in an epitaxial growth apparatus and method where a plurality of circular through-holes are formed in the bottom wall of a pocket in an outer peripheral region a distance of up to about ½ the radius toward the center of the circular bottom wall. The total opening surface area of these through-holes is 0.05 to 55% of the surface area of the bottom wall. The opening surface area of each of the through-holes provided at this outer peripheral region is 0.2 to 3.2 mm 2  and the density of the through-holes is 0.25 to 25 per cm 2 . After a semiconductor wafer is mounted in the pocket, epitaxial growth is carried out while source gas and carrier gas (i.e., reactive gas) is made to flow on the upper surface side of the susceptor and carrier gas is made to flow on the lower surface side.

FIELD OF THE INVENTION

This invention relates to a susceptor for epitaxial growth and anepitaxial growth method, and in particular relates to a susceptor forepitaxial growth and epitaxial growth technology for use in promotinggrowth of an epitaxial film on the surface of a semiconductor wafer.

BACKGROUND OF THE INVENTION

In recent years, epitaxial wafers where an epitaxial film is formed onthe surface of a silicon wafer are widely used as silicon wafers for usewith MOS devices. These epitaxial wafers provide improved yield for gateoxidation films of MOS devices, and have superior characteristics suchas the reduction of parasitic capacitance, the prevention of softerrors, improved gettering performance, and improved mechanicalstrength.

With this epitaxial wafer structure, in the prior art where a batchmethod is implemented so as to perform epitaxial growth processsimultaneously on a plurality of silicon wafers, it has become difficultto maintain compatibility with large diameter silicon wafers and singlewafer processing epitaxial growth apparatus have therefore mainly beenemployed. In recent years, epitaxial growth apparatus for use with largediameter wafers capable of performing epitaxial growth process on wafersof a diameter of 300 mm or more have been developed.

With these single wafer type epitaxial growth apparatus, methods oftransferring a wafer into and out of the apparatus, and onto asusceptor, can be classified into two types: a type where a wafer istransferred using a Bernoulli chuck method or elevating method using atransportation jig; and a type where the lower surface of the wafer issupported using pins, so that transfer is achieved by raising the pins.However, in each case, a semiconductor wafer is mounted on a singlesusceptor arranged horizontally in the apparatus. The wafer is thenraised to a high temperature using a heat source such as infrared lamps,etc. located around the wafer. Epitaxial growth is then initiated at thewafer surface by flowing a reactive gas over the surface of the wafer ata high-temperature while rotating the susceptor.

The following is a description, with reference to FIG. 19 to FIG. 23, ofa susceptor for epitaxial growth and an epitaxial growth method of theprior art.

FIG. 19 is a cross-sectional view schematically showing an epitaxialgrowth apparatus of the prior art. FIG. 20 is a plane view schematicallyshowing a susceptor for epitaxial growth of the prior art. FIG. 21 is afurther cross-sectional view schematically showing a susceptor forepitaxial growth of the prior art. FIG. 22 is a further cross-sectionalview schematically showing a design of a susceptor for epitaxial growthof the prior art. FIG. 23 is a further plane view schematically showingof a susceptor for epitaxial growth of the prior art.

As shown in FIG. 19 to FIG. 22, the epitaxial growth apparatus(hereinafter referred to as “apparatus”) 1 internally contains anepitaxial film forming chamber (hereinafter referred to as “film formingchamber”) 2. This film forming chamber 2 is equipped with an upper dome3, a lower dome 4, and a dome fitting 5. The upper dome 3 and the lowerdome 4 are made from a transparent material such as quartz, etc., with asusceptor 10 and silicon wafer W being heated using a plurality ofhalogen lamps 6 arranged above and below the apparatus 1.

The susceptor 10 is then rotated as a result of an outer part of thelower surface of the susceptor 10 engaging with a support arm 8 linkedto a susceptor rotating shaft 7. A carbon base material, coated on thesurface with a SiC film, is adopted as the susceptor 10. The susceptor10 is disc-shaped as shown in FIG. 20, or is disc-shaped having a recessas shown in FIG. 21, and supports the entire rear surface of the siliconwafer W. This recess is comprised of a pocket 10 a housing the siliconwafer W and is comprised of a substantially circular bottom wall and asidewall surrounding this bottom wall. A total of three through-holes 10b are formed every 120 degrees around the outside of the susceptor 10.Elevating pins 9 for raising and lowering the silicon wafer W areinserted loosely at each through-hole 10 b. Elevation of the elevatingpins 9 is carried out by a lift arm 11.

A gas supply opening 12 and gas exhaust opening 13 are located facingeach other at a position of the dome fitting 5 that faces the susceptor10. Reactive gas, that has been formed by diluting source gas such asSiHCl₃, etc. with hydrogen gas (carrier gas) and mixed with amicroscopic amount of dopant, is supplied from the gas supply opening 3so as to flow parallel (in a horizontal direction) to the surface of thesilicon wafer W. The provided reactive gas is exhausted to the outsideof the apparatus 1 by gas exhaust outlet 13 after passing over thesurface of the silicon wafer W to bring about epitaxial film growth.

In recent years, uniform distribution of resistivity within epitaxialfilm surfaces has become an extremely important quantitative requirementfor epitaxial wafers. However, high-temperature processing is requiredduring epitaxial growth. This causes dopant within the wafer to bediffused outwards during the epitaxial growth process and causes aso-called “autodoping” phenomenon where dopant is diffused outwards andis incorporated into the epitaxial film. This causes unevenness indopant concentration within the formed epitaxial film and causes theresistivity at the outer edge part of the epitaxial film to decrease,and resistivity distribution across the surface to be uneven. Inparticular, when epitaxial growth is carried out at a concentrationlower than the dopant concentration of the silicon wafer W, this causesregions where the dopant concentration of the epitaxial film is outsideof the required specifications to occur and causes device yield todecrease.

In order to prevent the deterioration of the resistivity distributionwithin the epitaxial film, silicon wafers are coated with a protectivefilm so that autodoping from the silicon wafer W is prevented. Siliconoxide films produced by CVD techniques are typically used as theprotective films for preventing autodoping and a polycrystaline siliconfilm formed on the rear surface of the wafer can contribute to getteringcapabilities and may also function as a protective film for reducingautodoping. Typically only the rear surface is coated with the siliconoxide film. The edges of the wafer are not coated, but any out diffusionof dopant from the wafer edge is minimal because of the small surfacearea.

The use of a wafer having a protective film is therefore effective insuppressing autodoping. However, this requires dedicated equipment suchas CVD processing tools, etc. and this requires additional processing.There are also cases that demand the use of an epitaxial wafer where theprotective layer must be removed from the rear surface after theepitaxial growth process. This requirement depends on the type ofprocessing required. In this case, it is necessary to perform additionalprocessing such as polishing and etching, etc. in order to remove theprotective film after the epitaxial growth process. This additionalprocessing causes the cost of producing epitaxial wafers to increase andin recent years this increased cost has made it impossible to producelow cost epitaxial wafers.

An epitaxial wafer that has been processed with an oxide backseal andthen the oxide stripped, has a dopant concentration at the rear surfacethat is similar to the bulk of the substrate. An epitaxial wafer thathas been processed without an oxide backseal has a rear surface that isdepleted of dopant concentration. This depleted rear surface may bebeneficial for subsequent processing by the device manufacturer. Inorder to resolve these problems, an epitaxial growth process method hasbeen proposed that employs a susceptor 10 formed with a large number ofthrough-holes 10 c over substantially the entire surface of the bottomwall of the pocket 10 a of the susceptor 10, as shown, for example, inFIG. 23.

However, when there are through-holes 10 c dispersed over substantiallythe whole surface of the bottom wall of the pocket, degradation of thenanotopology of the surface of the epitaxial wafer occurs due totemperature differences between regions where through-holes 10 c areformed and regions where through-holes 10 c are not formed and thesenanotopographical degradation regions occur across the entire wafersurface.

In the prior art, a region from a central position of the bottom wall ofthis pocket to a radius of ½ is a region for measuring the temperatureof the epitaxial growth process in the epitaxial growth apparatus. Whenthrough-holes 10 c are then formed in this region, variations occur inmeasurement of the process temperature and as a result there is anincreased possibility that slip will occur in the wafer.

On the other hand, uniform epitaxial film thickness is also an importantquantitative demand placed upon epitaxial wafers. The aforementionedreactive gas is supplied to the film-forming chamber 2 in a mannerparallel with respect to the surface of the silicon wafer W (FIG. 22).Part of the reactive gas flowing into the film-forming chamber 2therefore collides with the outer wall of the susceptor 10. As a result,the gas flow of reactive gas is disturbed in the vicinity of the upperedge part of the susceptor 10 and it is therefore difficult for thereactive gas to make sufficient contact with the outer edge surface ofthe silicon wafer W. As a result, this causes a phenomenon to occurwhere the epitaxial film of this portion becomes thin compared with thesurface portion. This phenomenon occurs regardless of whether or not aprotective film for preventing autodoping is present at the rear surfaceof the silicon wafer W.

Methods have therefore been disclosed in the prior art to preventlowering of film thickness at the outer parts of the epitaxial filmthrough control of the epitaxial growth process. To give concreteexamples, there is a method (1) where the speed of growth of anepitaxial film is lowered, and a method (2) where the height D from thesurface of the bottom wall of the susceptor 10 to the upper end surfaceof the sidewall is lowered. This height D is typically 0.55 to 1.00 mm.

However, according to the method (1) of lowering the growth speed, alonger period of time is required to grow the epitaxial film, and thisimpacts the productivity with which the silicon wafers are produced.Further, when the susceptor height D is lowered in (2), the siliconwafer W being processed may become miscentered in the pocket 10 a as theresult of small vibrations.

Moreover, the through-holes 10 c in the prior art are formed in adirection perpendicular to the bottom wall of the susceptor 10. When thethrough-holes are formed perpendicular to the susceptor pocket bottomwall, radiant heat can pass through the through-holes and can beabsorbed directly on the rear surface of the silicon wafer. This cancause non-uniform heating of the silicon wafer.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide anepitaxial growth susceptor and epitaxial growth method capable ofproviding uniformity with regards to film thickness of an epitaxialfilm, to reduce degradation regions regarding nanotopography of thesurface of an epitaxial wafer, to prevent the occurrence of slip of theepitaxial film caused by the forming of through-holes in the bottom wallof the pocket, to eliminate the influence of autodoping from the rearsurface of the wafer, and capable of improving uniformity of dopantconcentration within the epitaxial film surface.

It is a further object of the invention to provide an epitaxial growthsusceptor and an epitaxial growth method capable of improving theeffects of discharging dopant from the rear surface of the wafer.

It is still a further object of the invention to provide an epitaxialgrowth susceptor and an epitaxial growth method capable of preventingwafer contaminants originating from the susceptor base material.

Moreover, it is a still further object of this invention to provide anepitaxial growth susceptor and an epitaxial growth method whereepitaxial growth is carried out without forming a protective film on therear side of the wafer and to thereby lower the cost of the epitaxialwafer.

It is another object of this invention to provide an epitaxial waferwhere autodoping does not occur during thermal treatment in deviceprocessing.

It is a still further object of the invention to provide an epitaxialgrowth susceptor and an epitaxial growth method capable of suppressingvariations in radiant heat occurring at areas where through-holes areformed and capable of suppressing the occurrence of uneven brightness atthe rear surface of a semiconductor wafer.

SUMMARY OF THE INVENTION

In a first aspect of the invention, there is provided an epitaxialgrowth susceptor (hereinafter sometimes referred to simply as“susceptor”) with a pocket formed from a substantially circular bottomwall and a side wall encompassing the bottom wall, where a semiconductorwafer is to be mounted in the pocket. A plurality of through-holes withopenings that are substantially circular or polygonal are provided atthe bottom wall within an outer periphery region in a radial directionfrom the outer periphery of the bottom wall to the center, over adistance that is up to approximately {fraction (1/2)} of the radius,with the through-holes being included within at least a portion of theregion of the bottom wall on which the semiconductor wafer is mounted.The total opening surface area of the plurality of through-holes is 0.05to 55% of the surface area of the bottom wall.

Circular, elliptical or a similar shape may be given as substantiallycircular shapes. Triangular, quadrangular, pentagonal, or other angularshapes may be given as polygonal shapes.

The type of wafer is by no means limited. For example, a silicon waferor gallium arsenide wafer or SOI or selectively grown epitaxial wafersmay be used. If the total opening surface area of the plurality ofthrough-holes is smaller than 0.05% of the surface area of the bottomwall, dopant that diffuses outwards from the rear surface of the waferis not effectively exhausted. Further, when the total opening surfacearea exceeds 55%, slip begins to occur in the epitaxial wafer and thestrength of the susceptor itself decreases due to a temperaturedifference between the central part and outer periphery of the waferbeing large, and there are problems with the susceptor fracturing or thelike during the epitaxial reaction.

According to this first aspect of the invention, the plurality ofthough-holes are provided within an outer periphery region in a radialdirection from the outside of the bottom wall to the center over adistance that is up to ½ of the radius. The through-holes are includedwithin at least the region of the bottom wall on which the semiconductorwafer is mounted on. The total surface area of the openings of thethrough-holes is taken to be 0.05 to 55% of the surface area of thebottom wall. This improves uniformity of film thickness of the epitaxialfilm. Additionally, nanotopgraphically degraded regions of the epitaxialwafer surface that occur due to a temperature difference between theregions where a plurality of through-holes are formed in the bottom wallof the pocket and regions where the holes are not formed can bereduced., The slip caused by the forming of through-holes in the bottomwall of the pocket can also be prevented. Further, with semiconductorwafers where influence is exerted by autodoping from the rear surface ofthe wafer, it is possible to eliminate the influence of autodoping andto improve the uniformity of dopant concentration within the epitaxialfilm.

In a second aspect of this invention, in the epitaxial growth susceptorthere is further provided a support means at the bottom wall or sidewallfor supporting the mounted semiconductor wafer through surface contact,line contact or point contact with only the outer periphery of thesemiconductor wafer.

According to a susceptor structure where the entire rear surface of thesemiconductor wafer is surface-supported, it is difficult for carriergas such as hydrogen gas to become wrapped around the entire rearsurface of the wafer. The effectiveness with which dopant is dischargedfrom the rear surface of the wafer and is exhausted is thereforereduced. To this end, it is effective to form on the susceptor a supportmeans for supporting the wafer by making surface contact, line contactor point contact with the outer periphery of the wafer so that a slightgap is formed between the rear surface of the wafer and the uppersurface of the susceptor.

In a third aspect of the invention, a SiC film is adhered to the surfaceof the susceptor and to inner wall surfaces of each of thethrough-holes. Exposed surfaces of the susceptor and inner surfaces ofthe through-holes are coated with a SiC film. Contamination from thesusceptor base material, such as carbon contamination, etc., cantherefore be reliably prevented.

In a fourth aspect of the invention, at least the portion of thesusceptor that includes the through-holes of the susceptor is made of asolid SiC material.

The reason for making the portion of the susceptor that includes thethrough-holes of a solid SiC material is because it is difficult to coatall of the inside surfaces of the through-holes uniformly and becausepeeling of the SiC film tends to occur at parts of the inside surfacesof the through-holes. Contamination caused by the susceptor basematerial can be reliably prevented by forming the susceptor region wherethe through-holes are formed using a solid SiC material which isfabricated from solid SiC using a CVD technique, etc. It is alsopossible to form the entire susceptor from a solid SiC material.

In a fifth aspect of the invention, the through-holes of the susceptorare inclined with respect to the thickness direction of the bottom wall.

Namely, each of the through-holes is formed in the bottom wall inclinedin such a manner that a central axis of each through-hole is notorthogonal with respect to the bottom wall plane but rather has aprescribed angle. The angle of inclination of (the central axes of) thethrough-holes with respect to the bottom wall surface is, for example,20 to 70 degrees. The direction of inclination of the through-holes isby no means limited. Inclination from the upper surface of the bottomwall to the lower surface towards the inside of the bottom wall ortowards the outside is possible.

According to the fifth aspect of the invention, the radiant heatoccurring at the part of the bottom wall where the through-holes areformed can therefore be decreased compared with the case where thethrough-holes are not inclined and the occurrence of uneven brightnessat the rear surface of the semiconductor wafer can be suppressed.

In a sixth aspect of this invention, there is provided an expitaxialgrowth susceptor with a pocket formed from a substantially circularbottom wall and a sidewall encompassing the bottom wall, where asemiconductor wafer is to be mounted within the pocket. A plurality ofthrough-holes with openings that are substantially circular or polygonalare provided at the bottom wall within a region or a distance of up toapproximately {fraction (1/2)} the radius from the outer periphery tothe center in a radial direction, with the through-holes being includedwithin at least the region of the bottom wall on which the semiconductorwafer is to be mounted. The opening surface area of each through-hole istaken to be 0.2 to 3.2 mm², and the density of the through-holes istaken to be 0.25 to 25 holes per cm².

The reason the through-holes are not formed with an opening surface arealess than 0.2 mm² is because of technical difficulties with mechanicalmachining precision. When through-holes where the opening surface areaexceeds 3.2 mm² are formed, temperature distribution becomes uneven andnanotopographical degradation and the occurrence of slip becomes markeddue to the opening surface area being too large.

On the other hand, when the density of the through-holes is less than0.25 holes per cm², the amount of reactive gas flowing decreases andtherefore a decrease of the film thickness at the outer periphery of theepitaxial film cannot be prevented, the effectiveness with which dopantdischarged from the rear surface of the wafer is also small andtherefore the influence of autodoping cannot be eliminated. Whenthrough-hole density exceeds 25 per cm², the strength of the susceptoritself decreases and the susceptor may warp or fracture during theepitaxial growth process.

According to the sixth aspect of the invention, the thickness uniformityof the epitaxial film is improved and the nanotopgraphically degradedregions of the epitaxial wafer surface that occur due to a temperaturedifference between the regions where a plurality of through-holes areformed in the bottom wall of the pocket and regions where the holes arenot formed are reduced. The slip caused by the forming of through-holesin the bottom wall of the pocket can therefore be prevented. In the caseof semiconductor wafers where influence is exerted by autodoping fromthe rear surface of the wafer, it is also possible to eliminate theinfluence of this autodoping and to improve the uniformity of dopantconcentration within the epitaxial film surface.

In a seventh aspect of this invention, the epitaxial susceptor accordingto the sixth aspect of the invention is further provided with a supportmeans at the bottom wall or sidewall for supporting the mountedsemiconductor wafer through surface contact, line contact or pointcontact with only the outer periphery of the semiconductor wafer.

In an eighth aspect of the invention, a SiC film is adhered to thesurface of the susceptor of the sixth aspect of the invention and toinner wall surfaces of each of the through-holes.

In a ninth aspect of the invention, at least the portion of thesusceptor of the sixth aspect of the invention that includes thethrough-holes of the susceptor is made of a solid SiC material.

In a tenth aspect of the invention, the through-holes of the susceptorof the sixth aspect of the invention are inclined with respect to thethickness direction of the bottom wall.

In an eleventh aspect of the invention, there is provided an epitaxialgrowth method for growing an epitaxial film on a surface of asemiconductor wafer by mounting the semiconductor wafer within thesusceptor pocket and supplying source gas and carrier gas to an uppersurface side of the susceptor and supplying carrier gas to a lowersurface side of the susceptor. The pocket is formed from a substantiallyround bottom wall and a sidewall encompassing the bottom wall, and aplurality of through-holes with openings that are substantially circularor polygonal are provided at the bottom wall within a region or adistance of up to approximately {fraction (1/2)} the radius from theouter periphery to the center, with through-holes being included withinat least the region of the bottom wall on which the semiconductor waferis mounted. The total opening surface area of the plurality ofthrough-holes is 0.05 to 55% of the surface area of the bottom wall.

A gas such as, for example, SiH₄, SiH₂Cl₂, SiHCl₃ or SiCl₄ etc., isadopted as the source gas.

Hydrogen gas or an inert gas may be adopted as the carrier gas.

According to the eleventh aspect of the invention, after thesemiconductor wafer is mounted within the pocket, epitaxial growth iscarried out while flowing source gas and carrier gas on the uppersurface side of the susceptor and flowing carrier gas on the lowersurface side. Therefore, at the outer periphery of the susceptor, partof the source gas flowing on the upper surface side of the susceptorflows from a gap between the outer periphery of the semiconductor waferand the sidewall of the susceptor down to the lower surface side of thesusceptor via the through-holes as a result of negative pressure createdby the carrier gas flowing on the lower surface side of the susceptor. Asufficient amount of source gas can therefore be supplied to the surfaceof the outer periphery of the wafer. This improves the thicknessuniformity of the epitaxial film and reduces the nanotopographicallydegraded regions of the epitaxial wafer surface that occur due to atemperature difference between the regions where a plurality ofthrough-holes are formed in the bottom wall of the pocket and regionswhere the holes are not formed because the through-holes are not formedin the region from the center of the bottom wall of the susceptor to adistance of at least ½ of the radius from the center. The slip caused bythe forming of through-holes in the bottom wall of the pocket cantherefore be prevented.

Further, dopant is diffused outwards from the rear surface of a waferduring an epitaxial growth process when a semiconductor wafer with bothfront and rear surfaces constituted by a semiconductor single crystalsurface is subjected to the epitaxial growth process. However, in theeleventh aspect of the invention dopant is discharged at the lowersurface side of the susceptor due to the action of this negativepressure and it is difficult for this dopant to be incorporated into theepitaxial film. As a result, the influence of this autodoping from therear surface of the wafer can be substantially eliminated and theuniformity of dopant concentration within the epitaxial film surface canbe improved. This epitaxial growth process may also be applied tosemiconductor wafers with oxide films or polycrystalline films formed onthe rear surface thereof where the influence of autodoping is slight.Reduction in film thickness at the outer periphery of the epitaxial filmcan also be suppressed in this case.

In a twelfth aspect of this invention, there is further provided anepitaxial growth method where the epitaxial growth susceptor in theeleventh aspect of the invention is provided with support means at thebottom wall or sidewall for supporting the mounted semiconductor waferthrough surface contact, line contact or point contact with only theouter periphery of the semiconductor wafer.

In a thirteenth aspect of the invention, a SiC film is adhered to thesurfaces of the susceptor of the eleventh aspect of the invention and toinner wall surfaces of each of the through-holes.

In a fourteenth aspect of the invention, an epitaxial growth method isprovided where at least the portion of the susceptor of the eleventhaspect of the invention that includes the through-holes of the susceptoris made of a solid SiC material.

In a fifteenth aspect of the invention, an epitaxial growth method isprovided where the carrier gas supplied to the lower surface side of thesusceptor of the eleventh aspect of the invention is hydrogen containinggas supplied at 3 to 100 liters per minute.

When the amount of carrier gas flowing at the lower surface side of thesusceptor is less than 3 liters per minute, there is an insufficientamount of negative pressure generated and the dopant does noteffectively flow through the susceptor through-holes. In this case theautodoping is excessive. When a flow of 100 liters per minute flow isexceeded, the effectiveness of exhausting the dopant is increased, butthe carrier gas including the dopant is not discharged from the gasexhausting opening in an appropriate manner. Part of the carrier gasflows into the source gas and the distribution of resistivity within theepitaxial film deteriorates.

In a sixteenth aspect of the invention, an epitaxial growth method isprovided where the through-holes of the epitaxial growth susceptor ofthe eleventh aspect of the invention are inclined with respect to thethickness direction of the bottom wall.

In a seventeenth aspect of the invention, there is provided an epitaxialgrowth method for growing an epitaxial film on a surface of asemiconductor wafer by mounting the semiconductor wafer within thesusceptor pocket and supplying source gas and carrier gas to an uppersurface side of the susceptor and supplying carrier gas to a lowersurface side of the susceptor. The pocket is formed from a substantiallyround bottom wall and a sidewall encompassing the bottom wall, and aplurality of through-holes with openings that are substantially circularor polygonal are provided at the bottom wall within a region a distanceof up to approximately ½ the radius from the outer periphery to thecenter, with the through-holes being included within at least the regionof the bottom wall on which the semiconductor wafer is mounted. Theopening surface area of each through-hole is taken to be 0.2 to 3.2 mm²,and the density of the through-holes is taken to be 0.25 to 25 per cm².

According to the seventeenth aspect of the invention, after thesemiconductor wafer is mounted within the pocket of the susceptor,epitaxial growth is carried out while flowing source gas and carrier gason the upper surface side of the susceptor and flowing carrier gas onthe lower surface side. At this time, a negative pressure force acts atthe outer peripheral part of the susceptor due to carrier gas flowing onthe lower surface side of the susceptor causing part of the source gasflowing on the upper surface side of the susceptor to flow to the lowersurface side of the susceptor via the through-holes. As a result, asufficient amount of source gas can also be supplied to the surface ofthe outer periphery of the wafer, and the thickness of the epitaxialfilm can be made uniform. This uniformity of the epitaxial film cantherefore be achieved regardless of whether or not a protective film forpreventing autodoping is present at the rear surface of the siliconwafer. Nanotopographically degraded regions of the epitaxial wafersurface that occur due to a temperature difference between the regionswhere a plurality of through-holes are formed in the bottom wall of thepocket and regions where the holes are not formed can be reduced. Theslip caused by the forming of through-holes in the bottom wall of thepocket can be prevented.

Further, dopant is diffused outwards from the rear surface of the waferduring the epitaxial growth process in the case of a semiconductor waferwith both front and rear surfaces constituted by a semiconductor singlecrystal surface. However, dopant diffused outwards is exhausted to thelower surface side of the susceptor due to the action of the negativepressure. It is therefore difficult for the dopant to be taken into theepitaxial film. As a result, the influence of this autodoping from therear surface of the wafer can be eliminated and the uniformity of dopantconcentration within the epitaxial film surface can be improved.

In an eighteenth aspect of this invention, there is further provided anepitaxial growth method where the epitaxial growth susceptor of theseventeenth aspect of the invention is provided with a support unit atthe bottom wall or sidewall for supporting the mounted semiconductorwafer through surface contact, line contact or point contact with onlythe outer periphery of the semiconductor wafer.

In a nineteenth aspect of the invention, an epitaxial growth method isprovided where a SiC film is adhered to the surface of the susceptor ofthe seventeenth aspect of the invention and to inner wall surfaces ofeach of the through-holes in the epitaxial growth method.

In a twentieth aspect of the invention, an epitaxial growth method isprovided where at least the portion of the susceptor of the seventeenthaspect of the invention that includes the through-holes of the susceptoris made of a solid SiC material.

In a twenty-first aspect of the invention, an epitaxial growth method isprovided where the carrier gas supplied to the lower surface side of thesusceptor of the seventeenth aspect of the invention is hydrogencontaining gas supplied at 3 to 100 liters per minute.

In a twenty-second aspect of the invention, an epitaxial growth methodis provided where the through-holes of the susceptor of the seventeenthaspect of the invention are inclined with respect to the thicknessdirection of the bottom wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing an epitaxialgrowth apparatus on which is mounted an epitaxial growth susceptor of afirst embodiment of this invention.

FIG. 2 is an enlarged cross-sectional view schematically showing theessential parts of a usage state of a susceptor for epitaxial growth ofa first embodiment of this invention.

FIG. 3 is a plan view showing essential parts of a susceptor forepitaxial growth of a first embodiment of this invention.

FIG. 4 is an enlarged cross-sectional view showing essential parts of asusceptor for epitaxial growth of a first embodiment of this invention.

FIG. 5 is a plan view schematically showing a susceptor for epitaxialgrowth of a further embodiment of this invention.

FIG. 6 is a cross-sectional view schematically showing the essentialparts of a susceptor for epitaxial growth of a further embodiment ofthis invention.

FIG. 7 is a cross-sectional view schematically showing the essentialparts of a susceptor for epitaxial growth of a further embodiment ofthis invention.

FIG. 8 is a cross-sectional view schematically showing a susceptor forepitaxial growth of another embodiment of this invention.

FIG. 9 is a plan view schematically showing a susceptor for epitaxialgrowth of a further embodiment of this invention.

FIG. 10 is a cross-sectional view schematically showing essential partsof a susceptor for epitaxial growth of a still further embodiment ofthis invention.

FIG. 11 is a plan view schematically showing a susceptor for epitaxialgrowth of a further embodiment of this invention.

FIG. 12 is a graph showing distribution of dopant concentration in aradial direction of epitaxial films of epitaxial wafers obtained in atest example and a comparative example.

FIG. 13 is a graph showing distribution of resistivity in a radialdirection of epitaxial films of epitaxial wafers obtained in a testexample and a comparative example.

FIG. 14 is a graph showing changes in film thickness of epitaxial filmsof epitaxial wafers obtained in a test example and a comparativeexample.

FIG. 15 is a graph showing peak to valley (P-V) nanotopology occurringin the outer parts of epitaxial wafers obtained in a test example and acomparative example.

FIG. 16 is a graph showing the relationship between the surface area ofthe openings of through-holes and P-V nanotopography values forepitaxial wafers obtained in a test example and a comparative example.

FIG. 17 is a graph showing the relationship between the region from theedge of a wafer where through-holes are provided and the extent of adrop or decrease in thickness of an epitaxial film at the outer edge ofa wafer for epitaxial wafers obtained in a test example and acomparative example.

FIG. 18 is a graph showing the relationship between the surface area ofthe openings of the through-holes and the extent of slip for epitaxialwafers obtained in a test example and a comparative example.

FIG. 19 is a cross-sectional view schematically showing an epitaxialgrowth apparatus of the prior art.

FIG. 20 is a plan view schematically showing a susceptor for epitaxialgrowth of the prior art.

FIG. 21 is a further cross-sectional view schematically showing asusceptor for epitaxial growth of the prior art.

FIG. 22 is a further cross-sectional view schematically showing a usagestate of a susceptor for epitaxial growth of the prior art.

FIG. 23 is a further plan view schematically showing a usage state of asusceptor for epitaxial growth of the prior art.

PREFERRED EMBODIMENTS OF THE INVENTION

The following is a description of a susceptor for epitaxial growth andan epitaxial growth method of embodiments of this invention. The presentinvention is by no means limited by the following embodiments. FIG. 1 isa cross-sectional view schematically showing an epitaxial growthapparatus in which is mounted an epitaxial growth susceptor of a firstembodiment of this invention. FIG. 2 is an enlarged cross-sectional viewschematically showing essential parts of a usage state of a susceptorfor epitaxial growth of the first embodiment of this invention. FIG. 3is a plan view showing essential parts of a susceptor for epitaxialgrowth of the first embodiment of this invention. FIG. 4 is an enlargedcross-sectional view showing essential parts of a susceptor forepitaxial growth of the first embodiment of this invention.

FIG. 5 is a plan view schematically showing a susceptor for epitaxialgrowth of a further embodiment of this invention. FIG. 6 is across-sectional view schematically showing essential parts of asusceptor for epitaxial growth of the further embodiment of thisinvention. FIG. 7 is a cross-sectional view schematically showing theessential parts of a susceptor for epitaxial growth of the furtherembodiment of this invention.

As shown in FIG. 1 to FIG. 4, the epitaxial growth apparatus(hereinafter referred to as “apparatus”) 1 internally contains anepitaxial film forming chamber 2. This film forming chamber 2 isequipped with an upper dome 3, a lower dome 4, and a dome fitting 5. Theupper dome 3 and the lower dome 4 are made from a transparent materialsuch as quartz, etc., with a plurality of halogen lamps 6 for heating, asusceptor 10 and silicon wafer W arranged above and below the apparatus1. The silicon wafer W used is, for example, a P-type silicon singlecrystal wafer 200 mm in diameter, 740 μm thick, with surface planarorientation (100), a resistivity of 15 mΩcm (milli-ohm-cm) and with oneside having a mirrored finish. There is no silicon oxide film(protective film) formed on the rear side of the silicon wafer and bothsides of the wafer are single crystal silicon surfaces.

A gas supply opening 12 and gas exhaust opening 13 are located facingeach other at a position of the dome fitting 5 that faces the susceptor10. Reactive gas, that has been formed by diluting a source gas such asSiHCl₃ etc. with hydrogen gas (carrier gas) and mixed with a microscopicamount of dopant, is supplied from the gas supply opening 12 so as toflow parallel (in a horizontal direction) to the surface of the siliconwafer W. The provided reactive gas is exhausted to the outside of theapparatus 1 by a gas exhaust outlet 13 after passing over the surface ofthe silicon wafer W to bring about epitaxial film growth.

Further, at the dome fitting 5, a gas supply opening 14 for supplyingcarrier gas such as hydrogen gas, etc. is formed at the side of thelower surface of the susceptor 10 below the gas supply opening 12.Moreover, a gas exhaust opening 15 for exhausting hydrogen gas suppliedfrom the gas supply opening 14 to the outside is also provided at thedome fitting 5 in the vicinity below the gas exhaust outlet 13. It isalso possible to not provide the gas exhaust opening 15 and instead havethe gas exhaust outlet 13 also exhaust the carrier gas etc. forepitaxial growth.

A description is now given with reference to FIG. 2 to FIG. 4 of asusceptor 10 of this embodiment. This invention is, however, by no meanslimited to the susceptor 10.

The susceptor 10 is rotated as a result of an outer part of the lowersurface of the susceptor 10 engaging with a support arm 8 linking with asusceptor rotating shaft 7. This susceptor 10 has a pocket 1 a formedfrom a circular bottom wall of a diameter of up to 215 mm, which isslightly larger than the diameter of the silicon wafer W, and acylindrical sidewall surrounding the bottom wall. The bottom wall andsidewall are made from carbon materials with a SiC film adhered to thesurface. A silicon wafer is then housed in and mounted on this pocket 10a. The size of the susceptor can be changed in an appropriate manneraccording to the diameter of the silicon wafer W. To summarize, it ispreferable for the susceptor 10 to be of a size where there is a gap inthe order of 1 to 10 mm between the outer edge of the pocket 10 a andthe outer edge of the silicon wafer W. The depth of the pocket 10 a,i.e. the height from the upper surface of the bottom wall of thesusceptor 10 to the upper edge surface of the sidewall, is substantiallythe same as the thickness of the silicon wafer, at 800 μm. Further, atotal of three through-holes 10 b for pins that support and raise thesilicon wafer W up and down are arranged at 120 degree intervals in acircumferential direction at the outer periphery of the bottom wall.Elevating pins 9 for raising and lowering the silicon wafer W areinserted loosely at each of the three through-holes 10 b. Each elevatingpin 9 is provided so as to be raised and lowered freely with respect tothe support arm 8. The elevating pins 9 are raised and lowered by aplurality of lift arms 11 provided separately from the support arm 8 atthe susceptor rotating shaft 7 in such a manner as to enable raising andlowering.

Further, a plurality of through-holes 10 c are provided for preventingthe reduction of the epitaxial film grown at the outer periphery of thesurface of the wafer and for discharging dopant from the rear surface ofthe silicon wafer W that occurs at the outer periphery of the bottomwall. Specifically, through-holes 10 c are formed in a range 20 mm fromthe outer edge of the bottom wall of the pocket 10 a towards the insidein a radial direction of the wafer.

First, a description is given of the through-holes 10 b. Duringepitaxial growth, the elevating pins 9 are held within the through-holes10 b so that the insides of the through-holes 10 b are substantiallyclosed over. The through-holes 10 b therefore play little part asthrough-holes for discharging dopant. The through-holes 10 b for use inraising and lowering the wafer are not necessary for epitaxial growthapparatus where the wafer is transported using a Bernoulli chuck method,etc.

A combined function of through-holes 10 b as through-holes fordischarging dopant can also be achieved by providing recesses within thethrough-holes 10 b used for raising and lowering the wafer so that gasflows through (FIG. 5). Specifically, as shown in FIG. 6, there areslots supporting both ends (in the direction of the Y axis) of the headpart of an elevating pin 9 in a contacting manner, and, as shown in FIG.7, there are slots supporting both ends (in the direction of the X axis)of the head part of the elevating pin 9 in a non-contacting manner. Inthis case, it is preferable to subject the bottom wall surface layerpart of the pocket 10 a to mesh processing in order to promote gas flowwithin the through-holes 10 b.

Next, a description is given of the through-holes 10 c. Thethrough-holes 10 c are formed in the bottom wall (having a diameter of216 mm) so as to appear as circular holes as viewed from above. In theembodiment shown in FIG. 3, there are seven rows of holes and a total of834 holes. Each hole has a diameter of 1 mm, and an opening surface areaof 0.79 mm², and the density of the holes is 7.3/cm². The total openingsurface area of the through-holes 10 c is 1.8% of the surface area ofthe bottom wall. The through-holes 10 c are formed at least within theregion of the susceptor 10 above which the susceptor 10 is positioned.At least one row of holes and, preferably, at least two rows of holeshaving a size and density as described above are provided in thisregion. When through-holes 10 c are formed in the peripheral region(only outer side region of the wafer) of a susceptor 10 of a sizeexceeding the diameter of the wafer, the effects of discharging thedopant gas discharged from the rear surface of the wafer are reduced andthe influence of the autodoping cannot be eliminated.

As shown in FIG. 2 and FIG. 4, a support means 10 d supporting the outerperipheral part of the silicon wafer W in a line contact state isprovided at the bottom wall of the pocket 10 a in a tapered shapeinclined in a direction from the outside towards the inside (inclinedsurface). A space of at least 100 μm is therefore formed at a centralpart of the mounted silicon wafer W between the rear surface of thewafer and the bottom wall of the pocket 10 a. This promotes the wrappingaround of hydrogen gas to the rear surface of the wafer and enhances thedischarging of dopant from the rear surface of the wafer.

FIG. 8 is a cross-sectional view schematically showing a susceptor forepitaxial growth of another embodiment of this invention. FIG. 9 is aplane view schematically showing the susceptor for epitaxial growth ofFIG. 8. FIG. 11 is a plane view schematically showing the susceptor forepitaxial growth of another embodiment of this invention, in whichthrough-holes are formed at the bottom wall of the pocket 10 a and areconnected by a shallow channel 10 f.

As shown in FIG. 8, the support unit 10 d may also be configured so asto support the silicon wafer W. by making contact with the surface atjust the outer peripheral part of the silicon wafer. Uneven portions mayalso be provided on the surface of the support unit 10 d, with supportthen being achieved by point-contact between the surface and the outerperipheral part of the silicon wafer W.

The susceptor 10 of FIGS. 8 and 9 can be formed using differentmaterials for the bottom wall and the sidewall. Namely, the whole of thebottom wall of the pocket 10 a where the through-holes 10 c are formedusing a solid SiC material, and the sidewall of the pocket 10 a is acarbon base material coated with a SiC (silicon carbide) film. Carboncontaminants coming from the base material of the susceptor 10 can beeffectively eliminated using this coating.

In order to take into consideration the temperature distribution of theinner surface of the susceptor 10, the though-holes are formed over thewhole of an outer peripheral region in a radial direction from theoutside to the center of the bottom wall of the pocket 10 to a distancethat is approximately {fraction (1/2)} of the radius.

FIG. 10 is an example where through-holes 10 c formed in the outerperipheral region of the susceptor 10 are inclined by 45 degrees withrespect to the thickness direction of the bottom wall. The radiant heatcan therefore be suppressed in the region where the through-holes 10 care formed in the bottom wall by inclining the through-holes 10 c withina range of 20 degrees to 70 degrees with respect to the thicknessdirection of the bottom wall and the occurrence of uneven brightness ata rear surface of the silicon wafer W can be suppressed.

FIG. 11 is an embodiment of a susceptor of the present invention inwhich a row of through-holes is provided in the outer peripheral regionof the susceptor within the region of the susceptor on which the waferis mounted, with the holes being connected by a shallow channel, ortrench. The width of the trench is typically slightly greater than thediameter of the through-holes up to about 1.5 times the diameter. Thetrench has a depth such that the cross-sectional area of the trench isfrom about 50% to 100% of the opening surface area of a through-holeand, preferably, is close to that of a through-hole. From amanufacturing standpoint, the bottom of the trench is typically flat.This embodiment of the susceptor provides the following advantages. (1)Autodoping caused by dopant diffusing out from the wafer backside at theperiphery of the wafer can be effectively controlled by locating thethrough-holes only at the outer periphery of the wafer. (2) By locatingthe through-holes only at the periphery there is an improvement in thenanotopology at the center of the wafer, i.e., a reduction inthrough-holes produces improved nanotopology. (3) The trench provides agap between the wafer and susceptor at the periphery of the wafer whichprovides a path for improved mobility of dopant gas to be exhausted outthe through-holes. (4) Since the trench improves the mobility of thedopant gas, the density of through-holes can be further reduced and thisfurther improves nanotopology. (5) A shallow trench has a smaller impacton nanotopology degradation than a through-hole because there is stillsufficient susceptor mass to maintain a uniform thermal distributionwhich is a cause of nanotopology degradation. It is noted that althoughonly one row of holes is shown in FIG. 11, more than one row can beprovided.

TEST EXAMPLE AND COMPARATIVE EXAMPLE

A description will now be given of an epitaxial growth method for asingle wafer epitaxial growth apparatus mounted within a susceptor 10 asillustrated in FIG. 3.

First, a CZ silicon wafer W with the surface polished to a mirroredfinish in the usual manner is mounted within the pocket 10 a of thesusceptor 10.

Then, after the silicon wafer W is treated by baking in hydrogen at1150° C. for twenty seconds, a mixed reactive gas of a silicon sourcegas of SiHCl₃ and a boron source gas of B₂H₆ diluted in hydrogen gas issupplied to the apparatus 1 at a rate of 50 liters per minute so that aP-type epitaxial film of a thickness of approximately 6 μm andresistivity of 10 μm is formed on the wafer surface at an epitaxialgrowth temperature of 1070° C.

Reactive gas supplied from the reactive gas supply opening 12 passesthrough the film forming chamber 2 where the susceptor 10 and siliconwafer W are heated by a plurality of halogen lamps 6 arranged above andbelow the apparatus 1 and is exhausted from the apparatus 1 from the gasexhaust outlet 13 during the formation of the epitaxial film on thesurface of the silicon wafer W. Hydrogen gas is supplied from the gassupply opening 14 to within the film forming chamber 2 at a flow rate of15 liters per minute so as to pass through the lower surface side of thesusceptor 10 and after this, the hydrogen gas is exhausted from the gasexhaust opening 15.

In this case, a susceptor 10 (as shown in FIG. 3) is employed with aplurality of through-holes 10 c provided in the outer peripheral regionof the bottom wall so that the total opening surface area of thethrough-holes 10 c is 1.8% of the surface area of the bottom wall.Namely, after the silicon wafer W is mounted within the pocket 10 a,reactive gas is made to flow on the upper surface side of the susceptor10 and epitaxial growth then takes place while hydrogen gas is made toflow on the lower surface side. At this time, as shown in FIG. 2, anegative pressure force acts at the outer peripheral part of thesusceptor 10 due to the hydrogen gas flowing at the lower surface sideof the susceptor 10, and part of the reactive gas flowing at the uppersurface side of the susceptor 10 flows to the lower surface side of thesusceptor 10 via the through-holes 1 c. As a result, a large amount ofreactive gas comes into contact with the surface of the outer peripheralpart of the wafer. This improves the uniformity of the epitaxial filmand reduces the nanotopographically degraded regions of the epitaxialwafer surface that occur due to a temperature difference between theregions where a plurality of through-holes are formed in the bottom wallof the pocket and regions where the holes are not formed. The occurrenceof slip to the epitaxial film which can occur when through-holes areformed in the bottom wall of the pocket can therefore be prevented.

Further, a silicon oxide film for preventing autodoping is not formed atthe rear surface of the silicon wafer W and therefore both front andrear surfaces of the wafer can be configured from silicon single crystalsurfaces. Dopant (boron) is therefore diffused outwards from the rearsurface of the wafer during the epitaxial growth process. However,dopant diffused outwards is exhausted to the lower side of the susceptor10 due to the action of the aforementioned negative pressure force. Itis therefore difficult for the dopant to be taken into the epitaxialfilm. As a result, the dopant concentration of the epitaxial film islower than the dopant concentration of the silicon wafer W. Therefore,even in cases where the influence of autodoping from the rear surface ofthe wafer is substantial, this influence is eliminated and theuniformity of dopant concentration within the epitaxial film surface isimproved.

The results of comparing the test example of this invention based on theabove-described embodiment of this invention and a comparative exampleof the prior art are described below.

In the comparative example, as with the test example of this invention,the single wafer epitaxial growth apparatus shown in FIG. 1 is used andhydrogen gas is supplied at a rate of 15 liters per minute from the gassupply opening 14 in order to prevent silicon from becoming deposited onor in furnace members below the film-forming chamber 2 such as therotating shaft 7 of the susceptor 10. The susceptor 10 used is one asshown in FIG. 20.

Dopant concentration distribution in a radial direction within theepitaxial film, with the exception of the region from the outerperiphery to 3 mm, is measured using a surface charge profiler for theepitaxial silicon wafers obtained in the test example of this inventionand in the comparative example, respectively. The results are shown inthe graph in FIG. 12. Results obtained for resistivity distribution in aradial direction within an epitaxial film based on these measurementresults are shown in FIG. 13. FIG. 12 is a graph showing distribution ofdopant concentration in a radial direction of epitaxial films obtainedin the test example and the comparative example, and FIG. 13 is a graphshowing distribution of resistivity in a radial direction of epitaxialfilms obtained in the test example and the comparative example.

As is clear from FIG. 12 and FIG. 13, in the example of this invention,dopant is taken in in such a manner that dopant concentration within theepitaxial film is uniform in a radial direction and a p-type epitaxialfilm with a targeted resistivity of 10 Ωcm is obtained uniformly withinthe surface. On the other hand, dopant concentration is high at theouter periphery in the comparative example. It can also be understoodthat resistivity distribution falls accordingly by a substantial amountat the outer periphery.

Further, as shown in the graph in FIG. 14, the film thickness of theepitaxial film decreases at the outer periphery of the wafer andparticularly in the region from 2 to 3 mm from the outer edge. Thedeterioration substantially relates to deterioration in flatness in thefilm forming step for epitaxial film forming. FIG. 14 is a graph showingchanges in film thickness of epitaxial films of epitaxial wafersobtained in the test example and the comparative example.

With prior art susceptors, in the region from 2 to 10 mm from the outeredge of the wafer and more particularly in the region from 2 to 5 mmfrom the outer edge, the uniformity of film thickness of the epitaxialfilm deteriorates and the epitaxial film becomes dramatically thinner.The effect of this is that flatness (SFQR, etc.) after epitaxial growthis deteriorated substantially compared with flatness of the siliconwafer before epitaxial growth. With regards to this, the susceptor ofthis invention is capable of dramatically reducing the decrease in filmthickness of the epitaxial film that otherwise occurs at the outerperiphery of the wafer because using the susceptor of the presentinvention a sufficient amount of reactive gas is supplied to the edgeregions.

Next, a description is given based on FIG. 15 of how nanotopographicaldegradation of the wafer surface is improved by forming a plurality ofthrough-holes in only the outer peripheral region of the susceptor.

FIG. 15 is a graph showing nanotopography occurring in the outer partsof epitaxial wafers obtained in the test example and the comparativeexample. The nanotopology was measured by laser reflection angle fromthe wafer surface (as described in SEMI standard m43). In FIG. 15, theline graph for S=0 shows nanotopography for the case when a susceptorwith a through-hole opening surface area of 0 mm² is used, i.e., whenthere are no through-holes formed in the outer periphery of the bottomwall, and the line graph for S=3.14 shows nanotopography for when asusceptor with through-holes of an opening surface area of 3.14 mm²(diameter 2 mm) formed in the outer periphery of the bottom wall isused. When, for example, through-holes are dispersed over the whole areaof the bottom wall of the pocket, nanotopographical deteriorationoccurring due to temperature differences between regions wherethrough-holes are formed and regions where through-holes are not formedoccurs over the whole surface of the epitaxial wafer. However, in thepresent invention, through-holes are only formed in a region startingfrom the outside of the bottom wall to the center in a radial directionfor a distance of up to ½ the radius. The portion of regions where thereis no nanotopographical deterioration within the epitaxial wafer surfaceis therefore enlarged and a high-quality epitaxial wafer where thenumber of nanotopographically degraded regions has been reduced isobtained. A region from the center of the bottom wall of the susceptorto a radius of ½ is a region for measuring process temperature of theepitaxial growth apparatus. The through-holes are formed outside thisregion in this invention and the occurrence of slip to the epitaxialfilm can therefore be suppressed.

Next, the relationship between opening surface area of through-holes andP-V values for through-hole forming parts for the susceptor of thepresent invention and a prior art susceptor is shown in FIG. 16. As isclear from the relationship between the opening surface area and the P-Vvalue for the through-hole forming part, it is preferable for theopening surface area of the through-holes to be as small as possible soas to minimize the risk of nanotopographical degradation.

Next, a description is given using FIG. 17 of the relationship betweenthe region where the through-holes exist and the extent to which filmthickness of the epitaxial film decreases at the wafer edge region. FIG.17 is a graph showing the relationship between through-hole formingregions and an extent of a drop in film thickness of an epitaxial filmat outer parts of a wafer.

It can be understood from the graph of FIG. 17 that the dropping of filmthickness can be prevented when through-holes are provided in thevicinity from the outer peripheral edge of the pocket of the susceptorup to at least 50 mm inwards (i.e., up to approximately half the lengthof the radius from the outside of the bottom wall of the susceptor tothe center).

Next, a description is given of the through-hole opening surface areaand the amount of slip using the graph showing the relationship betweenopening surface area of through-holes and the extent of slip forepitaxial wafers as shown in FIG. 18.

Regarding the opening surface area of the through-holes, consideringcylindrical through-holes because of the limits of mechanical machiningprecision when forming the through-holes, it is considered not to bepossible to form through-holes of less than 0.2 mm². Problems withnanotopographical degradation and the occurrence of slip also placeconstraints on through-holes of 3.2 mm² or greater. An opening surfacearea for the through-holes of 3.2 mm² or less is therefore necessary togive nanotopographical degradation of 10 nm or less and to prevent theoccurrence of slip.

The rate of supplying reactive gas to the outer periphery of the waferis also substantially changed due to the relationship between thethrough-hole opening surface area and the through-hole density. It istherefore preferable to arrange the through-holes as densely as possiblein order that the influence of the flow of reactive gas to the lowerside of the susceptor shown in FIG. 1 is uniformly high with respect tothe circumferential direction of the wafer and in order to dramaticallysuppress the influence of autodoping and suppress reduction in epitaxialfilm thickness at the outer periphery of the wafer. The optimum rangefor the density of the through-holes is therefore 0.25 to 25 per cm² inorder to take into consideration problems with the strength of thesusceptor and through-hole machining precision.

A description has been given in the experimental example of a singlewafer epitaxial growth apparatus but this invention is by no meanslimited in this respect and may also be applied to batch methodepitaxial growth apparatus for treating a plurality of wafers at onetime as implemented in the related art. Additionally, the method of theinvention can also be applied to a Bernoulli chuck transfer apparatus.

As described above, according to this invention, the plurality ofthrough-holes is provided within an outer periphery region in a radialdirection from the outside of the bottom wall to the center over adistance that is up to about ½ of the radius, with the through-holesbeing included within at least the region of the bottom wall on whichthe semiconductor wafer is mounted. The total surface area of theopenings of the through-holes is 0.05 to 55% of the surface area of thebottom wall, the opening area of each through-hole is 0.2 to 3.2 mm² andthe opening density of through-holes is 0.25 to 25 per cm². Therefore,as a result, uniformity of thickness of the epitaxial film can beimproved and nanotopographically degraded regions of the epitaxial wafersurface that occur due to a temperature difference between the regionswhere a plurality of through-holes are formed in the bottom wall of thepocket and regions where the holes are not formed can be reduced.Additionally, slip to the epitaxial film caused by the forming ofthrough-holes in the bottom wall of the pocket can be prevented and theinfluence of autodoping from the rear surface of the wafer can beeliminated. Therefore, uniformity of dopant concentration within theepitaxial film surface can be improved.

In this invention, a support unit for supporting the mountedsemiconductor wafer through surface contact, line contact or pointcontact with only the outer periphery of the semiconductor wafer isprovided at the sidewall of the susceptor. Through-holes are provided inthe susceptor within a region from this contact toward the center. Thisprovides a substantial seal at the wafer edge and dopant, that isoutgassing from the wafer rear surface, diffuses out the through-holes.As a result, the influence of autodoping from the rear surface can beminimized.

Further, SiC films are adhered to the surface of the susceptor and theinner wall surfaces of each through-hole or at least the inner walls ofeach through-hole of the susceptor are made from an SiC material. Wafercontamination caused by the susceptor base material can therefore beprevented.

Moreover, in this invention an epitaxial wafer can be made that is notinfluenced by autodoping even without forming a protective film forpreventing autodoping at the rear surface of the wafer and, even incases where a semiconductor wafer with dopant added to a highconcentration is subjected to an epitaxial growth process, the cost ofproducing the epitaxial wafer can therefore be reduced.

According to the epitaxial growth method of this invention, dopant isdischarged to the outside from the rear surface of the wafer during anepitaxial reaction and it is therefore possible to provide an epitaxialwafer with extremely low dopant concentration at the rear surface of thewafer. This depleted rear surface may be beneficial for subsequentprocessing by device manufacturers. When the epitaxial growth susceptorof this invention is used, problems with autodoping and problems withimpurity contamination traceable to the susceptor structure aresubstantially resolved.

According to this invention, the through-holes may be inclined withrespect to the thickness direction of the bottom wall. Radiant heatoccurring at the part of the bottom wall where the through-holes areformed can therefore be suppressed, as can the occurrence of unevenbrightness at the rear surface of the semiconductor wafer.

1. An epitaxial growth susceptor comprising a substantially circularbottom wall and a sidewall encompassing the bottom wall to form a pocketfor mounting a semiconductor wafer, wherein a plurality of through-holeshaving a substantially circular or polygonal opening are provided in thebottom wall within a region of up to approximately half the radius ofthe bottom wall from the outer periphery to the center, in a radialdirection, with the through-holes being included within at least theregion of the bottom wall on which the semiconductor wafer is mounted;and a total opening surface area of the plurality of through-holes isbetween 0.05 to 55% of the surface area of the bottom wall.
 2. Theepitaxial growth susceptor of claim 1, further provided with a supportmeans at the bottom wall or the sidewall for supporting thesemiconductor wafer through surface contact, line contact or pointcontact with only the outer periphery of the semiconductor wafer.
 3. Theepitaxial growth susceptor of claim 1, wherein a SiC film is adhered toa surface of the susceptor and to inner wall surfaces of each of thethrough-holes.
 4. The epitaxial growth susceptor of claim 1, wherein atleast a portion of the bottom wall that includes the through-holes ismade of a solid SiC material.
 5. The epitaxial growth susceptor of claim1, wherein the through-holes are inclined with respect to the thicknessdirection of the bottom wall.
 6. An epitaxial growth susceptorcomprising a substantially circular bottom wall and a sidewallencompassing the bottom wall to form a pocket for mounting asemiconductor wafer, wherein a plurality of through-holes having asubstantially circular or polygonal opening are provided in the bottomwall within a region of up to approximately half the radius of thebottom wall from the outer periphery to the center, in a radialdirection, with the through-holes being included within at least theregion of the bottom wall on which the semiconductor wafer is mounted;and the opening surface area of each through-hole is taken to be between0.2 to 3.2 mm², and the density of the through-holes is taken to bebetween 0.25 to 25 per cm².
 7. The epitaxial growth susceptor of claim6, further provided with a support means at the bottom wall or sidewallfor supporting the semiconductor wafer through surface contact, linecontact or point contact with only the outer periphery of thesemiconductor wafer.
 8. The epitaxial growth susceptor of claim 6,wherein a SiC film is adhered to a surface of the susceptor and to innerwall surfaces of each of the through-holes.
 9. The epitaxial growthsusceptor of claim 6, wherein at least a portion of the bottom wall thatincludes through-holes is made of a solid SiC material.
 10. Theepitaxial growth susceptor of claim 6, wherein the through-holes areinclined with respect to the thickness direction of the bottom wall. 11.An epitaxial growth method for growing an epitaxial film on a surface ofa semiconductor wafer by mounting the semiconductor wafer within asusceptor pocket and supplying source gas and carrier gas to the uppersurface side of the susceptor and supplying carrier gas to the lowersurface side of the susceptor, wherein the susceptor comprises asubstantially circular bottom wall and a sidewall encompassing thebottom wall to form a pocket for mounting the semiconductor wafer,wherein a plurality of through-holes having a substantially circular orpolygonal opening are provided in the bottom wall within a region of upto approximately half the radius of the bottom wall from the outerperiphery to the center, in a radial direction, with the through-holesbeing included within at least the region of the bottom wall on whichthe semiconductor wafer is mounted.
 12. The epitaxial growth method ofclaim 11, further provided with a support means at the bottom wall orsidewall for supporting the semiconductor wafer through surface contact,line contact or point contact with only the outer periphery of thesemiconductor wafer.
 13. The epitaxial growth method of claim 11,wherein a SiC film is adhered to a surface of the susceptor and to theinner wall surfaces of each of the through-holes.
 14. The epitaxialgrowth method of claim 11, wherein at least a portion of the bottom wallthat includes the through-holes is made of a solid SiC material.
 15. Theepitaxial growth method of claim 11, wherein the carrier gas supplied tothe lower surface side of the susceptor is hydrogen-containing gassupplied at between 3 to 100 liters per minute.
 16. The epitaxial growthmethod of claim 11, wherein the through-holes are inclined with respectto the thickness direction of the bottom wall.
 17. An epitaxial growthmethod for growing an epitaxial film on a surface of a semiconductorwafer by mounting the semiconductor wafer within a pocket of a susceptorand supplying source gas and carrier gas to the upper surface side ofthe susceptor and supplying carrier gas to the lower surface side of thesusceptor, wherein the susceptor comprises a substantially circularbottom wall and a sidewall encompassing the bottom wall to form a pocketfor mounting the semiconductor wafer, wherein a plurality ofthrough-holes having a substantially circular or polygonal pattern areprovided in the bottom wall within a region of up to approximately halfthe radius of the bottom wall from the outer periphery to the center, ina radial direction, with the through-holes being included within atleast the region of the bottom wall on which the semiconductor wafer ismounted; and the opening surface area of each through-hole is taken tobe between 0.2 to 3.2 mm², and the density of the through-holes is takento be between 0.25 to 25 per cm².
 18. The epitaxial growth method ofclaim 17, further provided with a support means at the bottom wall orsidewall for supporting the semiconductor wafer through surface contact,line contact or point contact with only the outer periphery of thesemiconductor wafer.
 19. The epitaxial growth method of claim 17,wherein a SiC film is adhered to a surface of the susceptor and to theinner wall surfaces of each of the through-holes.
 20. The epitaxialgrowth method of claim 17, wherein at least a portion of the bottom wallthat includes the through-holes is made of a solid SiC material.
 21. Theepitaxial growth method of claim 17, wherein the carrier gas supplied tothe lower surface side of the susceptor is hydrogen-containing gassupplied at between 3 to 100 liters per minute.
 22. The epitaxial growthmethod of claim 17, wherein the through-holes are inclined with respectto the thickness direction of the bottom wall.
 23. An epitaxial growthsusceptor comprising a substantially circular bottom wall and a sidewallencompassing the bottom wall to form a pocket for mounting asemiconductor wafer, wherein a plurality of through-holes having asubstantially circular or polygonal opening are provided in the bottomwall within a region of up to approximately half the radius of thebottom wall from the outer periphery to the center, in a radialdirection, wherein at least one row of through-holes is included withinat least the region of the bottom wall on which the semiconductor waferis mounted, adjacent holes in a row of said at least one row ofthrough-holes being connected by a channel.
 24. The epitaxial growthsusceptor of claim 23, wherein said channel has a width that is up to1.5 times the diameter of a through-hole and a depth such that across-sectional area of a channel is from about 50% to about 100% anopening surface area of a through-hole.